The present invention relates to medical devices, and particularly to expandable medical devices such as cannulas, catheters, retractors, and similar devices.
Existing cannulas and/or retractors as used in endoscopic surgery today are passive devices which are fixed in length and width. They can not be varied intraoperatively in length and width to accommodate larger devices or varying size devices through the skin.
Skin and subcutaneous (subsurface) tissues are viscoelastic: they will gradually stretch without tearing. Once the tissue is slowly stretched it maintains its expanded condition for a period of time. Alternatively, the tissue can be stretched further, for example to progressively stretch out an incision. Then, after relaxation, the tissue will regain its original unstretched condition without having been damaged.
Current methods used for retracting tissue and improving visualization are mechanical separation using metal retractors during open surgery, or the direct pressure of an unconfined flow of fluid such as water or CO.sub.2 during fiberoptic surgery. A typical mechanical external fixator has pins driven through the bones and mechanically distracts the elements of the joint. Problems with the water method include fluid extravasation including into and through the tissue itself. Increased pressure and swelling result in the area, resulting in edematous or swollen tissue. Excess pressure from mechanical retractors may cause necrosis or tissue death. With these methods, it is impossible to monitor the pressure being applied to the body tissues, and tissue damage or necrosis can result.
While operating from within the body, i.e., fiber optic assisted surgery as opposed to open surgery, there is no known way to selectively move or retract tissue, either hard tissue such as bone or soft tissue, out of the way to improve visualization. No device in use adequately allows a surgeon to create an actual space or expand a potential space in the body, by separating adjacent layers of tissue. The prior art does not disclose a retractor which is powerful enough and made of a material which is strong and resilient enough to, for example, separate tissue planes from within. Such a device, especially in the field of fiber optic surgery, would allow a surgeon to visualize and operate without using the conventional bulky and awkward mechanical retractors which require large open incisions. Such a device would also permit working within the body without damaging a great deal of tissue in the path between the skin opening and the working area, by minimizing the external orifice or skin incision.